Mercury switch relay



Feb. 6, 1951 c, GEHRAND I 2,540,479

MERCURY SWITCH RELAY Filed Osc. 8, 1947 Patented Feb. 6, 1951 MERCURYSWITCH RELAY Clarence E. Gehrand, Elkhart, Ind., assignor to The AdlakeCompany, a corporation of Illinois Application October 8, 1947, SerialNo. 778,631

4 Claims.

This invention relates to mercury switch relays and has as its principalobject to provide a low resistance, non-arcing, hinged, electrical jointfor a contact element.

Generally speaking, this is accomplished by making a hinged joint forthe contact element swing about a bearin member such as a pin of copperor the like dipped in mercury to enclose it in a thin layer of amalgamand mercury which at once lubricates the hinge and makes alowresistance, non-arcing electrical connection through it.

Further objects and advantages of the invention will appear as thedisclosure proceeds and the description is read in connection with theaccompanying drawing in which Fig. l is a side view of a mercury switchrelay embodying the invention;

Fig. 2 is an end view looking from the right in Fig. 1;

Fig. 3 is a longitudinal section through the mercury switch envelopeshowing the working parts in elevation;

Fig. 4 is a longitudinal section through the relay including the workingparts;

Fig. 5 is a transverse section taken on the line 55 of Fig. 4;

Fig. 6 is a perspective view of the hinged contact bearing arm forming apart of the relay.

These drawings and the corresponding description are used for thepurpose of illustrative dis closure only, and are not intended to imposeunnecessary limitations on the claims.

General description This invention is an improvement on that dis-,closed in the application of Larson Serial No. 775,220, filed September20, 1947, now Patent No. 2,491,986, which application is acontinuation-inpart of Larson application, Serial No. 432,297, filedFebruary 25, 1942, now abandoned, and on that account the drawings andthe general disclosure are made to follow the Larson disclosure.

The relay is magnetically operated by a mechanism including a coil 3!having an L-shaped iron circuit 32, one leg of which extends over Themercury switch 39 is supported against the core 33 and the iron circuit32 by a clamp 4| attached to the iron circuit by a rivet 42 and havingcurved legs 43 extending around and firmly engaging the switch 39 tohold it in place.

The'mercury switch includes an envelope 46 (see Figs. 3 and 4) throughthe base of which are sealed electrodes or lead-ins ll and 48 shownencased partly in glass sleeves 49.

The lead-in or electrode 51 extends along the bottom of the envelope 46to cooperate with a mercury fill 61, normally retained in the positionshown in Figs. 3 and 4 by tilting the envelope as shown. The electrodeor lead-in 46 extends along the axis of the envelope 46 to about themidportion where it is fitted with a metal collar 5|, shrunk or weldedon and threaded on its outside as indicated at 52.

A cylindrical metal cap 53, having a central threaded bore 56, isscrewed over the collar 5|, as shown best in Fig. i, and made fast by alocking device consisting of a spring wire 51, having one end made fastin a transverse bore 55, and the other end bent to extend through a slot58 into contact with the threads 52 of the collar 51. The left end ofthe cap 53 is provided with a kerf 59 to receive a screw driver or othertool. The assembly of those parts will be apparent from the drawing, aswill also the fact that the locking device will retain the cap 53 inadjusted position with respect to the vertical plane extending throughthe axis of the lead-in 38.

The electrical circuit through the mercury switch is made and broken bycontact element 69, carried by a contact arm 64, hinged on the cap 53and operated in one direction by the magnet shown in Fig. 1. The hingeconnection for the contact arm is the important feature of thisinvention, and here is shown in an embodiment especially suitable forthe switch disclosed in the aforementioned application of Larson.

The contact arm 64 is provided with a pair of downwardly directed,spaced apart fingers 66, which span the cap 53 and are spaced from itsadjacent portions so as to prevent friction between those fingers andthe adjacent portions of the cap. Adjacent to the free end of eachfinger 66, it is punched out or counter-sunk at M to receive theadjacent end 15 of a hinge pin 16 extending through a transverse bore Hin the cap 53, and in this embodiment, the fingers 65 are bent towardseach other and compressed against the ends 15 of the pin It to make themgrasp it and bind it securely.

The pin 16 is preferably made of copper or notched at to receive asilencer 80. 1 shown as a fiattened tube forced over a tongue siloxane)like metal and fitted within the bore T! with a clearance of .003 to.004 of an inch, and before being inserted into the bore 11, it isliberally dipped in mercury, whereby it may be said to be pre-wetted,for apparently the mercury wets the copper, as it is said bymetallurgists, and forms with its outer portion an amalgam enclosing thepin, and itself enclosed in an excess of mercury which forms at once alubricant for the hinged joint and a low resistance electricalconnection through it. At least, this is believed to be the explanationof the character of joint formed by pre-dipping the copper pin inmercury and inserting it in the bore '11 with a clearance on the orderof .003 to .004 of an inch. The probable basis for this explanationappears in Encyclopaedia Britannica, 14th ed., page 724, vol. I.

Because the relay is operated magnetically, the contact arm 64 is madeof magnetic material such as iron, or its alloys, or a metal of the irongroup, and proper balance is attained by arranging the axis of the pin62 in the field of the iron circuit substantially as shown.

In order to prevent undesired magnetic effects from interfering with thequick operation of the switch, the thimble 53, and the collar 5i, shouldbe made of nonmagnetic material such as is commonly known as 18 and 8chromenickel-iron alloy, perhaps most generally referred to as stainlesssteel.

The right end of the contact bar 64 in Figs. 3 and 4, or the left end asit appears in Fig. 6 is It is 8! formed by the slots 6|. This silencermay be of any suitable material that does not amalgamate with themercury or injure the envelope 45. In this instance, it is made ofsilicone (poly rubber which is trimethyl silicone available in severalcolors and white is preferable. This material stands high temperature,is not affected by mercury, and. is sumciently resilient to cushion theblows of the bar 54 against the envelope 46 and the insulation 40. Otherrubber compositions and the like will be readily found available.

The gist of this invention appears to reside in making the hinged jointfor the contact element swing about a bearing member amalgamated withmercury and presenting suificient liquid to lubricate the hinge and formthe low resistance electrical conductor through it. Whether the amalgamis sufiiciently liquid to do this, or contains excess mercury sufficientto do this would appear to be immaterial. The proper characteristics areillustrated by pre-dipping a copper pin in mercury.

Other forms of hinged joint will readily occur to skilled designers.Some will use needle bearings, some pin bearings, some pintle bearings,and some pintles formed by balls or hemispherical elements, but theseand others are regarded as matters of choice.

In addition to the metals commonly known to V amalgamate with mercury,there are many alloys and platings that are amalgamable and suitable.Mention is here made of a few selected ones: (1) Everdur, which is analloy containing approximately 96% copper, 3% zinc, and 1% manganese,and characterized by high tensile strength on the order of 140,000pounds and low conductivity on the order of 6% of copper. The hightensile strength is important when the pin is assembled as heredescribed, for that will make it resist bending which might interferewith the free movement of the hinge. Generally speaking, materials forthe bearing should be selected for strength to hold the form and lowelectrical resistance. (2) Signal bronze, an alloy containingapproximately 97% copper, 2% tin, and 1% silicon, having a tensilestrength on the order of 100,000 pounds and a conductivity on the orderof of that of copper. (3) High strength bronze, an alloy containing98.8% copper and 1.2% tin, having a tensile strength on the order of40,000 pounds and conductivity approximately that of copper.

All of the electrical conducting parts should be chosen for lowconductivity where the characteristic of the switch is desired. Withsuch a selection and a hinged bearing such as described here, a mercuryswitch relay with .01'

ohm resistance may be had. This means that the relay can carry a heavyload without heating up, and hence will have long life.

In the operation of the switch shown in the drawing, it has beenobserved that mercury ap pears accumulated in the areas 85, Fig. 5,between the fingers 86, and the adjacent portions of the cap 55. Perhapsthese accumulations may be condensation of mercury vapor formed when thecircuit is opened and closed. At any rate, the mercury accumulationsappear in those areas and contribute to the high conductivity of theswitch or the low resistance through the hinge.

- In this Fig. 5, attempt is made to show the enthe switch, making itpossible to omit the predipping.

The amalgamation by pre-dipping the pin 16 may be accelerated by addinga small amount of commercial nitric acid to the mercury, but of course,pins given that treatment will have to be neutralized before use in theswitch.

I claim:

1. In a mercury switch, a switch envelop-e, a mercury fill in the switchenvelope, spaced electrodes in the switch envelope, and means forelectrically connecting said electrodes through said mercury fillincluding a contact member movable into and out of contact with saidmercury fill and a hinge for the contact member out of contact with themercury fill, and having a bearing part of amalgamable material dippedin mercury, whereby a thin coating of amalgam is formed on the bearingpart, said film constituting a lubricating and an electrical connectionthrough said hinge, the film being maintained by mercury vapor in theenvelope coming in contact with exposed portions of said amalgamablebearing part.

2. In a mercury switch, a switch envelope, a mercury fill in the switchenvelope, spaced electrodes in the switch envelope, and means forelectrically connecting said electrodes through said mercury fillincluding a contact member movable into and out of contact with saidmercury fill and a hinge for the contact member having a bearing part ofcopper, whereby mercury vapor within the envelope maintains a film ofamalgam over said bearing part to serve as a lubricating and electricalconnection through said hinge.

3. In a mercury switch, a switch envelope, a mercury fill in the switchenvelope, spaced electrodes in the switch envelope, and means forelectrically connecting said electrodes through said mercury fillincluding a contact member movable into and out of contact with saidmercury fill and a hinge for the contact member out of the mercury fillwhen the switch is closed, including fingers spanning and spaced from asupport, and a copper pin fitted closely through the support and graspedby the fingers, said pin being surrounded by a thin coating of amalgamwithin the support, and by washers of amalgam between the support andthe fingers.

4. In a mercury switch of the type having an envelope, a mercury filland spaced electrodes therein one of which is electrically disconnected6 with the mercury fill in the open position of the switch, a connectorfor the last mentioned electrode including a non-magnetic stainlesssteel support and a metal arm, both out of the mercury, and a hinge pinof copper dipped in mercury connecting the arm and the support.

CLARENCE E. GEI mAND.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,558,277 Phelan Oct. 20, 19251,897,454 Walker Feb. 14, 1933 2,116,215 Ruben May 3, 1938 Larson Dec.20, 1949

